zhack: add "action idle" subcommand

In order to reliably test the multihost protection we need two (or more)
systems attempting to import the pool at the same time.  Historically, we've
used ztest running in userspace to simulate an active pool and attempted to
import the pool with the kernel modules.  This works but ztest is a bit
unwieldy for this and if it crashes for unrelated reasons it can result
in false positives.

All we really need is the pool imported in userspace so the MMP thread is
active and writing out uberblocks.  We can extend zhack which already knows
how to import the pool read/write and add an option to leave the pool open
and idle.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Akash B <akash-b@hpe.com>

cmd/zhack.c

@@ -85,6 +85,10 @@ usage(void)
 	    "32-bit integer\n"
 	    "    -G               dump zfs_dbgmsg buffer before exiting\n"
 	    "\n"
+	    "    action idle <pool> [-f] [-t seconds]\n"
+	    "        import the pool for a set time then export it\n"
+	    "        -t <seconds> sets the time the pool is imported\n"
+	    "\n"
 	    "    feature stat <pool>\n"
 	    "        print information about enabled features\n"
 	    "    feature enable [-r] [-d desc] <pool> <feature>\n"
@@ -549,6 +553,79 @@ zhack_do_feature(int argc, char **argv)
 	return (0);
 }
 
+static void
+zhack_do_action_idle(int argc, char **argv)
+{
+	spa_t *spa;
+	char *target, *tmp;
+	int idle_time = 0;
+	int c;
+
+	optind = 1;
+	while ((c = getopt(argc, argv, "+t:")) != -1) {
+		switch (c) {
+		case 't':
+			idle_time = strtol(optarg, &tmp, 0);
+			if (*tmp) {
+				(void) fprintf(stderr, "error: time must "
+				    "be an integer in seconds: %s\n", tmp);
+				usage();
+			}
+			if (idle_time < 0) {
+				(void) fprintf(stderr, "error: time must "
+				    "not be negative: %d\n", idle_time);
+				usage();
+			}
+			break;
+		default:
+			usage();
+			break;
+		}
+	}
+	argc -= optind;
+	argv += optind;
+
+	if (argc < 1) {
+		(void) fprintf(stderr, "error: missing pool name\n");
+		usage();
+	}
+	target = argv[0];
+
+	zhack_spa_open(target, B_FALSE, FTAG, &spa);
+
+	fprintf(stdout, "Imported pool %s, idle for %d seconds\n",
+	    target, idle_time);
+	sleep(idle_time);
+
+	spa_close(spa, FTAG);
+}
+
+static int
+zhack_do_action(int argc, char **argv)
+{
+	char *subcommand;
+
+	argc--;
+	argv++;
+	if (argc == 0) {
+		(void) fprintf(stderr,
+		    "error: no import operation specified\n");
+		usage();
+	}
+
+	subcommand = argv[0];
+	if (strcmp(subcommand, "idle") == 0) {
+		zhack_do_action_idle(argc, argv);
+	} else {
+		(void) fprintf(stderr, "error: unknown subcommand: %s\n",
+		    subcommand);
+		usage();
+	}
+
+	return (0);
+}
+
+
 static boolean_t
 strstarts(const char *a, const char *b)
 {
@@ -1265,7 +1342,9 @@ main(int argc, char **argv)
 
 	subcommand = argv[0];
 
-	if (strcmp(subcommand, "feature") == 0) {
+	if (strcmp(subcommand, "action") == 0) {
+		rv = zhack_do_action(argc, argv);
+	} else if (strcmp(subcommand, "feature") == 0) {
 		rv = zhack_do_feature(argc, argv);
 	} else if (strcmp(subcommand, "label") == 0) {
 		return (zhack_do_label(argc, argv));